Using Kerberos Authentication

Using Kerberos Authentication

You can control access to Greenplum Database with a Kerberos authentication server.

Greenplum Database supports the Generic Security Service Application Program Interface (GSSAPI) with Kerberos authentication. GSSAPI provides automatic authentication (single sign-on) for systems that support it. You specify the Greenplum Database users (roles) that require Kerberos authentication in the Greenplum Database configuration file pg_hba.conf. The login fails if Kerberos authentication is not available when a role attempts to log in to Greenplum Database.

Kerberos provides a secure, encrypted authentication service. It does not encrypt data exchanged between the client and database and provides no authorization services. To encrypt data exchanged over the network, you must use an SSL connection. To manage authorization for access to Greenplum databases and objects such as schemas and tables, you use settings in the pg_hba.conf file and privileges given to Greenplum Database users and roles within the database. For information about managing authorization privileges, see Managing Roles and Privileges.

For more information about Kerberos, see http://web.mit.edu/kerberos/.

Requirements for Using Kerberos with Greenplum Database

The following items are required for using Kerberos with Greenplum Database:

  • Kerberos Key Distribution Center (KDC) server using the krb5-server library
  • Kerberos version 5 krb5-libs and krb5-workstation packages installed on the Greenplum Database master host
  • Greenplum Database version with support for Kerberos
  • System time on the Kerberos server and Greenplum Database master host must be synchronized. (Install Linux ntp package on both servers.)
  • Network connectivity between the Kerberos server and the Greenplum Database master
  • Java 1.7.0_17 or later is required to use Kerberos-authenticated JDBC on Red Hat Enterprise Linux 6.x
  • Java 1.6.0_21 or later is required to use Kerberos-authenticated JDBC on Red Hat Enterprise Linux 4.x or 5.x

Enabling Kerberos Authentication for Greenplum Database

Complete the following tasks to set up Kerberos authentication with Greenplum Database:

  1. Verify your system satisfies the prequisites for using Kerberos with Greenplum Database. See Requirements for Using Kerberos with Greenplum Database.
  2. Set up, or identify, a Kerberos Key Distribution Center (KDC) server to use for authentication. See Install and Configure a Kerberos KDC Server.
  3. In a Kerberos database on the KDC server, set up a Kerberos realm and principals on the server. For Greenplum Database, a principal is a Greenplum Database role that uses Kerberos authentication. In the Kerberos database, a realm groups together Kerberos principals that are Greenplum Database roles.
  4. Create Kerberos keytab files for Greenplum Database. To access Greenplum Database, you create a service key known only by Kerberos and Greenplum Database. On the Kerberos server, the service key is stored in the Kerberos database.

    On the Greenplum Database master, the service key is stored in key tables, which are files known as keytabs. The service keys are usually stored in the keytab file /etc/krb5.keytab. This service key is the equivalent of the service's password, and must be kept secure. Data that is meant to be read-only by the service is encrypted using this key.

  5. Install the Kerberos client packages and the keytab file on Greenplum Database master.
  6. Create a Kerberos ticket for gpadmin on the Greenplum Database master node using the keytab file. The ticket contains the Kerberos authentication credentials that grant access to the Greenplum Database.
With Kerberos authentication configured on the Greenplum Database, you can use Kerberos for PSQL and JDBC.
You can also configure external authentication for clients running on a Microsoft Windows system.

Install and Configure a Kerberos KDC Server

Steps to set up a Kerberos Key Distribution Center (KDC) server on a Red Hat Enterprise Linux host for use with Greenplum Database.

Follow these steps to install and configure a Kerberos Key Distribution Center (KDC) server on a Red Hat Enterprise Linux host.
  1. Install the Kerberos server packages:
    sudo yum install krb5-libs krb5-server krb5-workstation
  2. Edit the /etc/krb5.conf configuration file. The following example shows a Kerberos server with a default KRB.GREENPLUM.COM realm.
    [logging]
     default = FILE:/var/log/krb5libs.log
     kdc = FILE:/var/log/krb5kdc.log
     admin_server = FILE:/var/log/kadmind.log
    
    [libdefaults]
     default_realm = KRB.GREENPLUM.COM
     dns_lookup_realm = false
     dns_lookup_kdc = false
     ticket_lifetime = 24h
     renew_lifetime = 7d
     forwardable = true
     default_tgs_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
     default_tkt_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
     permitted_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
    
    [realms]
     KRB.GREENPLUM.COM = {
      kdc = kerberos-gpdb:88
      admin_server = kerberos-gpdb:749
      default_domain = kerberos-gpdb
     }
    
    [domain_realm]
     .kerberos-gpdb = KRB.GREENPLUM.COM
     kerberos-gpdb = KRB.GREENPLUM.COM
    
    [appdefaults]
     pam = {
        debug = false
        ticket_lifetime = 36000
        renew_lifetime = 36000
        forwardable = true
        krb4_convert = false
     }
    

    The kdc and admin_server keys in the [realms] section specify the host (kerberos-gpdb) and port where the Kerberos server is running. IP numbers can be used in place of host names.

    If your Kerberos server manages authentication for other realms, you would instead add the KRB.GREENPLUM.COM realm in the [realms] and [domain_realm] section of the kdc.conf file. See the Kerberos documentation for information about the kdc.conf file.

  3. To create a Kerberos KDC database, run the kdb5_util.
    kdb5_util create -s
    The kdb5_util create option creates the database to store keys for the Kerberos realms that are managed by this KDC server. The -s option creates a stash file. Without the stash file, every time the KDC server starts it requests a password.
  4. Add an administrative user to the KDC database with the kadmin.local utility. Because it does not itself depend on Kerberos authentication, the kadmin.local utility allows you to add an initial administrative user to the local Kerberos server. To add the user gpadmin as an administrative user to the KDC database, run the following command:
    kadmin.local -q "addprinc gpadmin/admin"
    Most users do not need administrative access to the Kerberos server. They can use kadmin to manage their own principals (for example, to change their own password). For information about kadmin, see the Kerberos documentation.
  5. If needed, edit the /var/kerberos/krb5kdc/kadm5.acl file to grant the appropriate permissions to gpadmin.
  6. Start the Kerberos daemons:
    /sbin/service krb5kdc start
    /sbin/service kadmin start
  7. To start Kerberos automatically upon restart:
    /sbin/chkconfig krb5kdc on
    /sbin/chkconfig kadmin on

Create Greenplum Database Roles in the KDC Database

Add principals to the Kerberos realm for Greenplum Database.

Start kadmin.local in interactive mode, then add two principals to the Greenplum Database Realm.
  1. Start kadmin.local in interactive mode:
    kadmin.local
  2. Add principals:
    kadmin.local: addprinc gpadmin/kerberos-gpdb@KRB.EXAMPLE.COM
    kadmin.local: addprinc postgres/master.test.com@KRB.EXAMPLE.COM
    The adprinc commands prompt for passwords for each principal. The first addprinc creates a Greenplum Database user as a principal, gpadmin/kerberos-gpdb. The second addprinc command creates the postgres process on the Greenplum Database master host as a principal in the Kerberos KDC. This principal is required when using Kerberos authentication with Greenplum Database.
  3. Create a Kerberos keytab file with kadmin.local. The following example creates a keytab file gpdb-kerberos.keytab in the current directory with authentication information for the two principals.
    kadmin.local: xst -k gpdb-kerberos.keytab
        gpadmin/kerberos-gpdb@KRB.EXAMPLE.COM
        postgres/master.test.com@KRB.EXAMPLE.COM
    You will copy this file to the Greenplum Database master host.
  4. Exit kadmin.local interactive mode with the quit command:
    kadmin.local: quit

Install and Configure the Kerberos Client

Steps to install the Kerberos client on the Greenplum Database master host.

Install the Kerberos client libraries on the Greenplum Database master and configure the Kerberos client.
  1. Install the Kerberos packages on the Greenplum Database master.
    sudo yum install krb5-libs krb5-workstation
  2. Ensure that the /etc/krb5.conf file is the same as the one that is on the Kerberos server.
  3. Copy the gpdb-kerberos.keytab file that was generated on the Kerberos server to the Greenplum Database master host.
  4. Remove any existing tickets with the Kerberos utility kdestroy. Run the utility as root.
    sudo kdestroy
  5. Use the Kerberos utility kinit to request a ticket using the keytab file on the Greenplum Database master for gpadmin/kerberos-gpdb@KRB.EXAMPLE.COM. The -t option specifies the keytab file on the Greenplum Database master.
    # kinit -k -t gpdb-kerberos.keytab gpadmin/kerberos-gpdb@KRB.EXAMPLE.COM
  6. Use the Kerberos utility klist to display the contents of the Kerberos ticket cache on the Greenplum Database master. The following is an example:
    # klist
    Ticket cache: FILE:/tmp/krb5cc_108061
    Default principal: gpadmin/kerberos-gpdb@KRB.EXAMPLE.COM
    Valid starting     Expires            Service principal
    03/28/13 14:50:26  03/29/13 14:50:26  krbtgt/KRB.GREENPLUM.COM     @KRB.EXAMPLE.COM
        renew until 03/28/13 14:50:26

Set up Greenplum Database with Kerberos for PSQL

Configure a Greenplum Database to use Kerberos.

After you have set up Kerberos on the Greenplum Database master, you can configure Greenplum Database to use Kerberos. For information on setting up the Greenplum Database master, see Install and Configure the Kerberos Client.
  1. Create a Greenplum Database administrator role in the database template1 for the Kerberos principal that is used as the database administrator. The following example uses gpamin/kerberos-gpdb.
    psql template1 -c 'create role "gpadmin/kerberos-gpdb" login superuser;'
    
    The role you create in the database template1 will be available in any new Greenplum Database that you create.
  2. Modify postgresql.conf to specify the location of the keytab file. For example, adding this line to the postgresql.conf specifies the folder /home/gpadmin as the location of the keytab file gpdb-kerberos.keytab.
    krb_server_keyfile = '/home/gpadmin/gpdb-kerberos.keytab'
    
  3. Modify the Greenplum Database file pg_hba.conf to enable Kerberos support. Then restart Greenplum Database (gpstop -ar). For example, adding the following line to pg_hba.conf adds GSSAPI and Kerberos support. The value for krb_realm is the Kerberos realm that is used for authentication to Greenplum Database.
    host all all 0.0.0.0/0 gss include_realm=0 krb_realm=KRB.GREENPLUM.COM
    For information about the pg_hba.conf file, see The pg_hba.conf file in the Postgres documentation.
  4. Create a ticket using kinit and show the tickets in the Kerberos ticket cache with klist.
  5. As a test, log in to the database as the gpadmin role with the Kerberos credentials gpadmin/kerberos-gpdb:
    psql -U "gpadmin/kerberos-gpdb" -h master.test template1
    
    A username map can be defined in the pg_ident.conf file and specified in the pg_hba.conf file to simplify logging into Greenplum Database. For example, this psql command logs into the default Greenplum Database on mdw.proddb as the Kerberos principal adminuser/mdw.proddb:
    $ psql -U "adminuser/mdw.proddb" -h mdw.proddb
    If the default user is adminuser, the pg_ident.conf file and the pg_hba.conf file can be configured so that the adminuser can log in to the database as the Kerberos principal adminuser/mdw.proddb without specifying the -U option:
    $ psql -h mdw.proddb

    The following username map is defined in the Greenplum Database file $MASTER_DATA_DIRECTORY/pg_ident.conf:

    # MAPNAME   SYSTEM-USERNAME        GP-USERNAME
    mymap       /^(.*)mdw\.proddb$     adminuser

    The map can be specified in the pg_hba.conf file as part of the line that enables Kerberos support:

    host all all 0.0.0.0/0 krb5 include_realm=0 krb_realm=proddb map=mymap

    For more information about specifying username maps see Username maps in the Postgres documentation.

  6. If a Kerberos principal is not a Greenplum Database user, a message similar to the following is displayed from the psql command line when the user attempts to log in to the database:
    psql: krb5_sendauth: Bad response
    The principal must be added as a Greenplum Database user.

Set up Greenplum Database with Kerberos for JDBC

Enable Kerberos-authenticated JDBC access to Greenplum Database.

You can configure Greenplum Database to use Kerberos to run user-defined Java functions.
  1. Ensure that Kerberos is installed and configured on the Greenplum Database master. See Install and Configure the Kerberos Client.
  2. Create the file .java.login.config in the folder /home/gpadmin and add the following text to the file:
    pgjdbc {
      com.sun.security.auth.module.Krb5LoginModule required
      doNotPrompt=true
      useTicketCache=true
      debug=true
      client=true;
    };
  3. Create a Java application that connects to Greenplum Database using Kerberos authentication. The following example database connection URL uses a PostgreSQL JDBC driver and specifies parameters for Kerberos authentication:
    jdbc:postgresql://mdw:5432/mytest?kerberosServerName=postgres
    &jaasApplicationName=pgjdbc&user=gpadmin/kerberos-gpdb
    The parameter names and values specified depend on how the Java application performs Kerberos authentication.
  4. Test the Kerberos login by running a sample Java application from Greenplum Database.